None.
The present invention is a moat feature for achieving high-integrity, airtight seals between an optical apparatus block and the components attached to the block.
One embodiment of this invention is applied to a ring laser gyroscope (RLG). A RLG is commonly used to measure the angular rotation of a vehicle, such as an aircraft. Such a gyroscope has two counter-rotating laser light beams which move within a closed loop path or xe2x80x9cringxe2x80x9d with the aid of successive reflections from multiple mirrors. The closed path is defined by an optical cavity which is interior to a structural gyroscope frame or xe2x80x9cblockxe2x80x9d. In one type of RLG, the block includes planar top and bottom surfaces that are bordered by six planar sides that form a hexagon-shaped perimeter. Surfaces on each of the sides define mounting areas for components such as mirrors and electrodes. For example, three planar non-adjacent sides of the block form the mirror mounting surfaces for three mirrors at the corners of the optical path, which is triangular in shape.
Operationally, upon rotation of the RLG about its input axis (which is perpendicular to and at the center of the planar top and bottom surfaces of the block), the effective path length of each counter-rotating laser light beam changes, and a frequency differential is produced between the beams that is nominally proportional to angular rate. This differential is then measured by signal processing electronics to determine the angular rotation of the vehicle.
Typically in a RLG block having a triangular shaped optical path incorporating three mirrors, one of the mirrors has a concave reflective surface while the other two mirrors have planar reflective surfaces. The curved mirror serves two main purposes. First, the curvature of the reflective surface controls the diameter and the primary mode of the counter-rotating laser light beams. Second, the curvature of the reflective surface is used to align the counter-rotating laser light beams within the optical cavity so that the light beams are at substantially maximum intensity to minimize RLG bias errors. In particular, this latter purpose is accomplished due to the inherent attributes of the concave reflective surface. Additionally, a typical RLG block has three electrodes, which are disposed one on each of the three planar side surfaces not occupied by mirrors.
It is important that the mirrors and electrodes are securely attached to their respective surfaces, and that the seal between the block and those components is airtight so that a vacuum inside the block is preserved. Typically, the components are soldered onto their respective planar surfaces. However, these surfaces often contain scratches, chips, and fractures, formed during manufacture or handling, which prevent the formation of an airtight seal. There is a need for an improved device and method for achieving a high integrity seal between a RLG block and the components attached thereto.
The present invention is a device and method for achieving an airtight seal between a RLG block and the components attached thereto. The invention comprises disposing a centered annular ring, or moat, on each of the six planar sides of a RLG block. The surface of each moat is slightly below the surrounding surface of each side of the block. Because each moat is depressed relative to the respective side surface, the moat surface is less likely to become scratched, and therefore allows for a better seal between the block and the mirror or electrode attached thereto.